Floating, stinging, punching, prophesying, he transformed his sport and became the world's most adored athlete

Oliver Wendell Holmes once observed that every profession is great that is greatly pursued. Boxing in the early '60s, largely controlled by the Mob, was in a moribund state until Muhammad Ali--Cassius Clay, in those days--appeared on the scene. "Just when the sweet science appears to lie like a painted ship upon a painted ocean," wrote A.J. Liebling, "a new Hero...comes along like a Moran tug to pull it out of the ocean."

Though Ali won the gold medal at the Rome Olympics in 1960, at the time the experts didn't think much of his boxing skills. His head,...